The present invention relates generally to current sensing devices for electrical systems, and more particularly to resettable alternating current fault indicators.
Various types of self-powered fault indicators have been constructed for detecting electrical faults in power distribution systems, including clamp-on type fault indicators, which clamp directly over cables in the systems and derive their operating power from inductive coupling to the monitored conductor, and test point type fault indicators, which are mounted over test points on cables or associated connectors of the systems and derive their operating power from capacitive coupling to the monitored conductor. Such fault indicators may be either of the manually reset type, wherein it is necessary that the indicators be physically reset, or of the self-resetting type, wherein the indicators are reset upon restoration of line current. Examples of such fault indicators are found in products manufactured by E.O. Schweitzer Manufacturing Company of Mundelein, Ill., and in U.S. Pat. Nos. 3,676,740, 3,906,477, 4,063,171, 4,234,847, 4,375,617, 4,438,403, 4,456,873, 4,458,198, 4,495,489, 4, 4,974,329, and 5,677,678 of the present inventor.
Detection of fault currents in fault indicators is typically accomplished by means of magnetic switch means such as a magnetic reed switch in close proximity to the conductor being monitored. Upon occurrence of an abnormally high fault-associated magnetic field around the conductor, the magnetic switch actuates a trip circuit which produces current flow in a trip winding to position an indicator flag visible from the exterior of the indicator to a trip or fault indicating position. Upon restoration of current in the conductor, a reset circuit is actuated to produce current flow in a reset winding to reposition the target indicator to a reset or non-fault indicating position.
In certain applications, such as where the fault indicator is installed in a dark or inaccessible location, the need arises for a light indication in addition to the flag indication. Repair crews can then more easily find the location of the fault.
Because of the compact construction and limited power available in self-powered fault indicators it is preferable that the light indication be provided with minimal additional circuitry and structure within the fault indicator while providing reliable and extended operation following occurrence of a fault. The present invention is directed to a novel fault indicator light circuit which meets the above requirements by utilizing a magnetic winding, such as the actuator winding of the electro-mechanical indicator flag assembly typically utilized in fault indicators, in conjunction with a magnetic circuit to connect an internal battery upon occurrence of a fault.
Accordingly, it is a general object of the present invention to provide a new and improved fault indicator having a light indication of fault occurrence.
It is a more specific object of the present invention to provide a new and improved self-powered fault indicator which provides a light indication for an extended period of time following occurrence of a fault current in a monitored conductor.
It is a still more specific object of the present invention to provide a fault indicator wherein a light-indication is provided utilizing the electromagnetic flag indicator assembly of the fault indicator in conjunction with an internal battery.
The invention is directed to a fault indicator for indicating the occurrence of a fault current in an electrical conductor. The fault indicator comprises a housing, a battery, a lamp operable from the battery and viewable from the exterior of the housing, a magnetic circuit including a magnetic pole piece, a magnetically actuated switch and a bias magnet, the bias magnet having a magnetic polarity which opposes a magnetic field in the magnetic pole piece in one direction, and reenforces a magnetic field in the magnetic pole piece in the other direction, whereby the magnetically actuated switch is conditioned to open in response to a magnetic field in the one direction and closed in response to a magnetic field in the other direction, means including a magnetic winding in magnetic communication with the magnetic pole piece and responsive to the current in the monitored conductor for developing a magnetic field in the magnetic pole piece in the one direction to condition the switch open during normal current flow in the monitored conductor, and for developing a magnetic field in the magnetic pole piece in the opposite direction to condition the switch closed upon occurrence of a fault current in the conductor, the magnetically actuated switch connecting the battery to the lamp whereby the lamp lights in the fault indicating state.
The invention is further directed to a fault indicator for indicating the occurrence of a fault current in an electrical conductor. The fault indicator comprises a housing, a battery, a lamp operable from the battery and viewable from the exterior of the housing, an indicator flag assembly including an indicator flag viewable from the exterior of the housing and a first magnetic pole piece, the indicator flag being magnetized and in magnetic communication with the first magnetic pole piece whereby the indicator flag is actuated to a reset-indicating position by a magnetic field in the first magnetic pole piece in one direction, and is actuated to a fault-indicating position by a magnetic field in the first magnetic pole piece in the opposite direction, a second magnetic pole piece, a magnetically actuated switch and a bias magnet, the bias magnet having a magnetic polarity which opposes magnetic field in the second magnetic pole piece in one direction, and reenforces magnetic field in the second magnetic pole piece in the other direction, whereby the magnetically actuated switch is actuated open in response to a magnetic field in the one direction and closed in response to a magnetic field in the other direction, means including a magnetic winding in magnetic communication with the first and second magnetic pole pieces and responsive to the current in the monitored conductor for developing a magnetic field in the one direction in the pole pieces to position the indicator flag in the reset indicating position and condition the magnetically actuated switch in the first state during normal current flow in the monitored conductor, and for developing a magnetic field in the opposite direction in the pole pieces to position the indicator flag in the fault indicating position and condition the magnetically actuated switch closed upon occurrence of a fault current in the conductor, the magnetically actuated switch connecting the battery to the lamp whereby the lamp lights in the fault indicating state.